Gas generating cartridge



Sept. 14, 1954 w, JARVIS 2,688,920

GAS GENERATING CARTRIDGE Filed D80. 29, 1952 2 Sheets-Sheet 1 l2 H l0 IO l0 l2 H K) IO '0 1 I V 7 xi: 1/7 .A. [3

IN VEN TOR ATTORNEYS Sept. 14, 1954 Filed Dec. 29, 1952 F. W. JARVIS GAS GENERATING CARTRIDGE 2 Sheets-Sheet 2 INVEWTOR. m

ATTORNEYS.

Patented Sept. 14, 1954 UNITED STATES OFFICE I 2,688,920 GAS GENERATING CARTRKDGE Application December 29, 1952, Serial No. 328,331

Claims priority, application Great Britain 7 July 24, 1952 8 Claims. 1 The present invention relates to an improved power gas-generating cartridge for the actuation of an engine starter of the kind wherein the gases generated by the cartridge impinge on the blades of the turbine of the starter.

Modern military aircraft engine starters of the aforesaid kind often require a starter. cartridge which contains in addition to a single cylindrical annular charge with exposed internal and external cylindrical surfaces and end surfaces of a horny substantially ashless self-combustible composition based on colloided nitrocellulose containing nitroglycerine and suitable cooling and stabilising ingredients also igniting elements such that the flash for instance from an electrically actuated igniter is transmitted to the cylindrical annular charge through a small charge of a readily ignitible loose granular kindling composition such as blackpowder, retained in close proximity to the said igniter and contained in an easily destructible container.

As in practice it is possible only to produce said nitrocellulose compositions which can support their own combustion satisfactorily and efficiently at pressures substantially higher than the working pressure of the turbine of the engine starter, there is provided in the engine starter a pressure controlling nozzle interposed between the cartridge breech and the turbine chamber. It is important that this nozzle should not become obstructed and that the blades of the turbine should not be damaged by projection from the cartridge of any loose uncombusted or incombustible components of the cartridge in the form of particles of any substantial weight and dimensions. It is also important that the nozzle should not become obstructed by the forward movement of the annular charge at any stage during its combustion.

Furthermore the designing of a cartridge as aforesaid particularly for an aeroplane engine starter of the aforesaid kind is made more difiicult because cartridges may be subjected to vibration and rough usage in handling. This vibration and rough usage are liable to cause damage to the aforesaid easily destructible container and to the aforesaid loose granular kindling composition.

The provision therefore of spacing members to prevent displacement of the annular charge within a cartridge of the aforesaid kind for use in engine starters of the aforesaid kind has heretofore presented a difficult problem because the spacing members have to be provided in the cartridge by simple and convenient operations in manufacture and the possibility of their projection from the cartridge into the pressure control- 2 ling nozzle or on to the blades of the turbine of the engine starter must be absent.

A cartridge for an engine starter in accordance with the present invention of the kind comprising a rigid metal cartridge case having at its base an igniter and containing a cylindrical annular main charge of a colloided nitrocellulose composition capable of supporting its own combustion and having exposed internal and external cylindrical surfaces and end surfaces and also containing a charge of a granular kindling composition enclosed in an easily destructible container of flimsy construction interposed between the igniter and the base of said main charge is characterised in that the base of the said annular main charge has projecting therefrom stilts of self-combustible colloided nitrocellulose composition bearing against the base of the cartridge case to form a chamber for the enclosed kindling composition and spaced so as to provide free flame gas passage from the basal to the cylindrical surfaces of said main charge, in that a portion of the length of said annular charge has projections of self-combustible colloided nitrocellulose composition bearing against the cylindrical wall of the cartridge case and spaced to provide free gas passage along the outer cylindrical surf-ace, in that a top portion of said annular charge is held within the legs of an indestructible spider member having an outer diameter substantially approaching the internal diameter of the cartridge case, and in that the top portion of the cartridge case is so turned over as to prevent said spider member from forward motion and to allow a free gas passage out of the container.

The stilts of self-combustible colloided nitrocellulose composition projecting from the base of said cylindrical annular main charge prevent this main charge from rearward axial motion towards the cartridge case and thus protect the kindling composition from damage.

Said indestructible spider member prevents said annular main charge from having forward axial motion even while it is burning.

It is essential that the face of said spider which bears on at least a portion of the end surface of the annular charge should be of such design as to continue to bear against at least a portion of the resulting end surface which is present throughout the burning of the charge.

The main charge is prevented against radial movement both by said projections of a selfcombustible colloided nitrocellulose composition and by the legs of said spider member.

Said stilts and projections may be made of a composition which gives on burning a gas at a higher temperature than the compositions of the main charge in order to facilitate ignition of said main charge.

If desired the ignition of a portion of the outer cylindrical surface may be retarded by providing it with an adherent temporary coating of nonself-combustible or relatively less easily self-combustible film.

The stilts projecting from the annular cylinder may be preformed and cemented to the surface of the annular cylinder. They may consist of the same composition as the material of the annular cylinder, but a faster or slower burning composition may be used provided it is self-combustible. The easily 'destructible container of the kindling composition may be in the form of a textile bag or a thin container of plastic material. It is I found in practice that the fragments of a thin cotton bag or a thin film of cellulose acetate or the like pass through the pressure controlling nozzle of the engine starter and between the blades of the turbine without damaging the latter. The kindling powder may consist of grained black-powder.

The cartridge is sealed at the forward end against the entry of moisture with a disc of thin material such as Celluloid or cellulose acetate, and may further be provided at this end with a temporary protecting cap.

Two forms of cartridges in accordance with the invention are illustrated in Figs. 1 to 4 of the diagrammatic drawings accompanying the specification, whereof Figs. 1 and 2 represent part. ly axially sectioned views, Fig. 3 is a plan taken on the line A-A of Fig. 2 looking towards the cartridge base and Fig. 4 is a right section through line B-B, looking in the same direction.

Referring to Figs. 1 and 2, the cartridge case is made of brass and is drawn with a'thick base I which is outwardly flanged to fit into a breech in the engine starter. The almost cylindrical Wall 2 of the cartridge case is thinner than the base and is shaped to ensure a close fit in the breech, which is continuously tapered. From the interior of the cartridge base there is pressed into place an igniter housing 3 containing an electrical igniter 4 charged with fine grain blackpowder held in place by small thin Celluloid disc ll. On top of this igniter is a muslin bag containing loose a kindling charge of a coarser grain of blackpowder 5, this bag having been cemented to a substantial portion of the area of the base To the external cylindrical surface of the annular charge 1 there have been similarly attached studs 8 of the same composition as the composition 9. These studs are spaced in two staggered rows each of three studs at an angle of 120, one row being near the end of the annular cylinder bearing 9, and the other somewhat more than half way along its length. These studs are of sufficient thickness to enable the charge to fit snugly within the cartridge case. The axial flame gas channel is best seen at 15 in Fig. 4 and as will be seen from Figs. 1, 2 and 4 there is also provided a radial channel I4 in communication with this axial channel. The purpose of this is to relieve any excessive pressure within the axial flame gas channel l5. In the cartridge illustrated in Fig. 2 to a portion of the external cylindrical surface beyond the uppermost stud 8 there is cemented a wrapping of an overlapping spiral of adherent regenerated cellulose tape 16.

Embracing the forward end of the annular charge is a steel spider having a continuous annular discoid web II] from which project arms Ill. These arms extend outwardly and are then bent over so that a portion of their length is perpendicular to the plane of the web. It will be seen that as the arms lil' spring from the continuous annular web 10 they are first slightly bent in a forward direction before they are bent rearwardly, so that the forward surface of the spider is slightly dished with reference to the summit of the bend of the arms. The rearwardly bent-over portion of the arms Ii) ofthe spider can just be slipped over the end of the annular charge in the case of Fig. 1, or the wrapping of the forward portion of the annular charge in the case of Fig. 2, and thethickness of this bent over portion of the arms is only slightly less than the depth of the free space between the, outer cylindrical surface of the annular charge and the cartridge case. The central hole in the Web Ill is of greater diameter thanthe axial gas channel 15 of the annular charge I and it will be understood from the preceding account that the external diameter of the web 10 is smaller than that of the said annular charge, so that there is a free gas passage from the space between the wall 2 of the cartridge case and the outer cylindrical surface of the charge .1 into the portion of the cartridge of the charge. 1 around the igniter 4 and extending over the latter. I is a single piece annular cylindrical charge extruded hot from a composition consisting mainly of nitrocellulose and nitroglycerine with lesser proportions of dibutyl phthalate, diethyl diphenyl urea, mineral jelly and potassium nitrate. This annular charge is considerably greater in length than in thickness. To the base of this annular charge there have been cemented at angles of 120 three stilts 9, of colloided nitrocellulose-nitroglycerine composition of faster burning characteristics than the composition of the annular cylinder 1. The cement used for the purpose may be made by dissolving some of the composition from which the stilts 9 are formed in acetone. It will be seen that the free ends of the stilts 9 bear against the interior surface of the base of the cartridge case and stilt the base of the annular charge 1 so as to provide just sufficient space for the bag 6 containing the blackpowder charge 5 so that its contents have only a small free movement.

forward of the web ll] of the spider. A light cellulose acetate sealing cup H is. placed over the spider and provided with a sealing cement on its upper surface before the forward end of the cartridge case is turnedover the angle of the spider arms as shown at [2, so that the turn-over brings about a waterproof seal and retains the spider even after the cartridge has been used. i3 is a stout removeable metal end-cap for protecting the mouth of the case and the cellulose acetate sealing cup I i from mechanical damage.

When the cap l3 has been removed, and the cartridge has been thrust into the breech, and the breech closure has been effected and the electrical firing circuit hasbeen completed by the operator, the charge of fine grain blackpowder in the electrical igniter 4 is ignited and immediately burns through the Celluloid disc ll, and brings aboutignition of. the kindling charge of coarser blackpowderii in the muslin bag 6. Flame gases'from the blackpowder charge 5 sweep along theaxial gas channel It of the annular charge 1 and also sweep past the stilts 9 into the channel between the outer cylindrical surface of .the charge land theJwall 2 of the cartridge case, sweeping past the stud-s 8 attached to the cylindrical surface of the former. These stilts and studs tendto assist commencement of the ignition of the surface of the charge I itself. The flame gases sweep around the charge I and through its axial gas channels l5 into the space between the web ID of the spider and the sealing cup ll, quickly burst the latter and bring about its disruption into harmless fragments, which pass through the nozzle and the blades of the turbine without damage to the latter. During the combustion of the charge 7 its internal and external diameter and length diminish, but the spider I0 prevents the partly consumed annulus from being shot bodily forward out of the cartridge since the spider is held by the turn-over of the cartridge case at the angle l2 where its legs are bent over. Before the charge has burned away the studs and stilts 8 and 9 will of course have been entirely consumed and all that is left after the charge 7 is burned away is the spider.

In the form of the cartridge illustrated in Fig. 2 the ignition of part of the outer cylindrical surface of the charge 1 is somewhat delayed by the presence of the wrapping of adhesive regenerated cellulose tape, but this is soon broken down and destroyed by action of the flame gases and the charge thereafter burns on both its internal and. external cylindrical surfaces throughout its whol length.

What I claim is:

l. A cartridge for an engine starter of the kind comprising a rigid metal cartridge case having at its base an igniter and containing a cylindrical annular main charge of a colloided nitrocellulose compositioncapable of supporting its own combustion and having exposed internal and external cylindrical surfaces and end surfaces and also containnig a charge of a granular kindling composition enclosed in an easily destructible container of flimsy construction interposed between the igniter and the base of said main charge characterised in that the base of the annular main charge has projecting therefrom stilts of self-combustible colloided nitrocellulose composition bearing against the base of the cartridge case to form a chamber for the enclosed kindling composition and spaced so as to provide free flame gas passage from the basal to the cylindrical surfaces of said main charge, in that a portion of the length of said annular charge has projections of self-combustible colloided nitrocellulose composition bearing against the cylindrical wall of the cartridge case and spaced to provide free gas passage along the outer cylindrical surface, in that an indestructible spider member having an outer diameter substantially approaching the internal diameter of the cartridge case positioned within said cartridge case and a top portion of said annular charge is held within the legs of said spider member and in that the top portion of the cartridge case is so turned over as to prevent said spider member from forward motion and to allow a free gas passage out of the container.

2. A cartridge as claimed in claim 1 wherein said stilts and projections are of a composition which gives on burning a gas at a higher temperature than the composition of the main charge.

3. A cartridge as claimed in claim 1 wherein the outer cylindrical surface is provided with an adherent temporary coating of a non-selfcombustible film.

4. A cartridge as claimed in claim 1 wherein the outer cylindrical surface is provided with an adherent temporary coating of a relatively less easily self-combustible film.

5. A cartridge as claimed in claim 1 wherein the stilts are preformed and cemented to the surface of the annular cylinder.

6. A cartridge as claimed in claim 1 wherein the easily destructible container of the kindling composition is in the form of a textile bag.

7. A cartridge as claimed in claim 4 wherein the easily destructible container of the kindling composition is formed of a thin film of plastic material.

8. A cartridge as claimed in claim 1 provided at its forward end with a temporary protecting cap.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,464,181 Lauristen Mar. 8, 1949 FOREIGN PATENTS Number Country Date 594,012 Great Britain Oct. 31, 1947 

